#include <bits/stdc++.h>

using namespace std;

#define debug(x) cerr << #x << " = " << x << "\n";

using ll = long long;

ifstream in("bmatrix.in");
ofstream out("bmatrix.out");

const int maxN = (int)2e2 + 5;

int n, m;

char mat[maxN][maxN];

int hist[maxN];

char aux[maxN][maxN];

int solveHistogram() {
  int ans = 0;
  stack<int> st;
  hist[m + 1] = hist[0] = 0;
  st.push(0);
  for (int i = 1; i <= m + 1; i++) {
    while ((int)st.size() > 0 && hist[st.top()] > hist[i]) {
      int top = st.top();
      st.pop();
      ans = max(ans, hist[top] * (i - st.top() - 1));
    } 
    st.push(i);
  }
  return ans;
}
  
int solve(int start, int end) {
  int ans = 0;
  for (int i = 0; i <= max(n, m); i++) {
    hist[i] = 0;
  }
  for (int i = start; i <= end; i++) {
    for (int j = 1; j <= m; j++) {
      if (mat[i][j] == '0') {
        hist[j]++;
      } else {
        hist[j] = 0;
      }
    }
    ans = max(ans, solveHistogram());
  }
  return ans;
}

int main() {
  in >> n >> m;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      in >> mat[i][j];
    }
  }
  int ans = 0;
  for (int rep = 0; rep < 2; rep++) {
    for (int line = 1; line < n; line++) {
      ans = max(ans, solve(1, line) + solve(line + 1, n));
    }
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= m; j++) {
        aux[j][i] = mat[i][j];
      }
    }
    swap(n, m);
  }
  out << ans << "\n";
  return 0;
}